Slurry composition, electrode and secondary cell

ABSTRACT

A slurry composition for electrode comprising a binder, an active material, and a liquid medium, characterized in that the binder comprises a polymer (X) comprising 60 to 95 mole % of repeating units derived from acrylonitrile or methacrylonitrile and 5 to 30 mole % of repeating units derived from at least one kind of a monomer selected from 1-olefins and compounds represented by the following general formula (1): CH 2 ═CR 1 —COOR 2  wherein R 1  represents a hydrogen atom or a methyl group and R 2  represents an alkyl group; and the liquid medium is capable of dissolving the polymer (X). The slurry composition allows the manufacture of a lithium ion secondary battery having enhanced capacity and good charge-discharge cycle characteristics and good charge-discharge rate characteristics.

TECHNICAL FIELD

This invention relates to a slurry composition for electrode, anelectrode made using the slurry composition, and a secondary batteryprovided with the electrode.

BACKGROUND ART

In recent years, portable electronic appliances such as a notebook-sizedpersonal computer, a cellular phone and a personal digital assistancehave spread wide. Recently prolongation of service time of portableelectronic appliances and shortening of charging time (i.e., improvementof rate characteristics) thereof are eagerly desired. To fulfill thesedesires, requirements for rendering high in performance of battery,especially enhancing the capacity and the rate of charge, are becomingsevere.

A lithium ion secondary battery has a structure such that a positiveelectrode and a negative electrode with a separator interposed betweenthe electrodes are placed together with an electrolyte liquid in avessel. The positive electrode and the negative electrode are made bybonding an electrode active material (hereinafter referred to merely as“active material” when appropriate) and an optional electricalconductivity-imparting agent and other ingredients to a collector madeof, for example, aluminum or copper through a binder for electrode(hereinafter referred to as “binder” when appropriate). The bonding ofan electrode material to the collector is conducted by a procedurewherein an active material and other optional ingredients are mixed witha solution or dispersion of a binder in a liquid medium to prepare aslurry composition for an electrode of lithium ion secondary battery; acollector is coated with the slurry composition; and the liquid mediumis removed from the thus-formed liquid coating, for example, by drying,to form a mixed material layer comprising the active material on thecollector.

The capacity of a battery greatly depends upon the amount of an activematerial filled in the electrode. The rate characteristics of a batteryvary depending upon the ease in movement of electrons, and the ratecharacteristics can be enhanced by an increase of the amount of anelectrical conductivity-imparting agent such as carbon. To increase theamount of an active material and the amount of an electricalconductivity-imparting agent within a limited space of battery, theamount of a binder must be minimized. However, minimization of theamount of binder results in reduction of bonding force of the activematerial. Therefore, a binder exhibiting an enhanced bonding force evenwhen it is used in a minor amount is eagerly desired.

Heretofore, a fluorine-containing polymer such as polyvinylidenefluoride has been widely used as a binder for a positive electrode of alithium ion secondary battery. However, the fluorine-containing polymerdoes not have a sufficiently high bonding force and flexibility, andtherefore, enhancement in the capacity of battery and the ratecharacteristics thereof is difficult to attain.

To remedy the drawbacks of a fluorine-containing polymer, a polymerrubber has been proposed as a binder in Japanese Unexamined PatentPublication No. H4-255670. A polymer rubber exhibits good bonding forceand flexibility when an electrode is made using the polymer rubber, but,the cycle characteristics of battery are poor, and the capacity ofbattery is reduced and the rate characteristics are deteriorated, atrepetition of a charge-discharge cycle. This would be due to the factthat the binder is swollen with an electrolyte liquid, and consequently,the bonding force of binder is gradually reduced and an active materialtends to be separated from a collector, and the binder undesirablycovers the entire surface of collector leading to reduction in amovement of electrons.

Thus, it has been difficult to enhance both of the capacity of batteryand the rate characteristics thereof.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a slurry compositioncontaining a binder having a reduced degree of swelling with anelectrolyte liquid and an enhanced bonding force; and an electrode madeusing the slurry composition.

Another object of the present invention is to provide a secondarybattery having an enhanced capacity and good rate characteristics.

The present inventors have found that a binder comprised of a specificcopolymer comprising acrylonitrile or methacrylonitrile units andspecific 1-olef in units or acrylic or methacrylic acid ester units hasa reduced degree of swelling with an electrolyte liquid and an enhancedbonding force; and further that a lithium ion secondary batterymanufactured using a slurry composition for electrode comprising thebinder has an enhanced capacity and exhibits improved cyclecharacteristics and good rate characteristics, at repetition of acharge-discharge cycle. The present invention has been completed on thebasis of these findings.

Thus, in accordance with the present invention, the following slurrycompositions (1), (2), (3) and (4) are provided.

(1). A slurry composition for electrode comprising a binder, an activematerial for electrode, and a liquid medium, characterized in that thebinder comprises a polymer (X) comprising 60 to 95% by mole of repeatingunits derived from acrylonitrile or methacrylonitrile and 5 to 30% bymole of repeating units derived from at least one kind of a monomerselected from 1-olefins and compounds represented by the followinggeneral formula (1):CH₂═CR¹—COOR²   (1)wherein R¹ represents a hydrogen atom or a methyl group and R²represents an alkyl group; and the liquid medium is capable ofdissolving the polymer (X).

(2). A slurry composition for an electrode as described above in (1),wherein the binder further comprises a polymer (Y) having a glasstransition temperature in the range of −80 to 0° C. and containing notlarger than 5% by weight of N-methyl-pyrrolidone-insoluble matter, andthe ratio in content of the polymer (X) to the polymer (Y) is in therange of 1/10 to 10/1 by weight.

(3). A slurry composition for electrode as described above in (1),wherein the binder further comprises a polymer (Z) having a glasstransition temperature in the range of −80 to 0’ C. and containing atleast 50% by weight of N-methyl-pyrrolidone-insoluble matter, and theratio in content of the polymer (X) to the polymer (Z) is in the rangeof 1/10 to 10/1 by weight.

(4). A slurry composition for electrode as described above in (1),wherein the binder further comprises a polymer (Y) and a polymer (Z),and the ratio in content of the sum of the polymer (X) plus the polymer(Y) to the polymer (Z) is in the range of 5/1 to 1/5 by weight.

The above-mentioned slurry compositions (1) through (4) are preferablyused for making a positive electrode of a lithium ion secondary battery.

The above-mentioned liquid medium is preferably N-methyl-pyrrolidone.

The above-mentioned polymer (Y) is preferably a hydrogenation product ofan acrylonitrile-butadiene copolymer, and the above-mentioned polymer(Z) is preferably an acrylic rubber.

Further, in accordance with the present invention, the followingelectrodes (5), (6), (7) and (8) and a secondary battery (9) areprovided.

(5). An electrode comprising a mixed material layer comprising at leasta binder and an active material for electrode, which layer is bonded toa collector, characterized in that the binder comprises a polymer (X)comprising 60 to 95% by mole of repeating units derived fromacrylonitrile or methacrylonitrile and 5 to 30% by mole of repeatingunits derived from at least one kind of a monomer selected from1-olefins and compounds represented by the following general formula(1):CH₂═CR¹—COOR²   (1)wherein R¹ represents a hydrogen atom or a methyl group and R²represents an alkyl group; and the liquid medium is capable ofdissolving the polymer (X).

(6). An electrode as described above in (5), wherein the binder furthercomprises a polymer (Y) having a glass transition temperature in therange of −80 to 0° C. and containing not larger than 5% by weight ofN-methyl-pyrrolidone-insoluble matter, and the ratio in content of thepolymer (X) to the polymer (Y) is in the range of 1/10 to 10/1 byweight.

(7). An electrode as described in (5), wherein the binder furthercomprises a polymer (Z) having a glass transition temperature in therange of −80 to 0° C. and containing at least 50% by weight ofN-methyl-pyrrolidone-insoluble matter, and the ratio in content of thepolymer (X) to the polymer (Z) is in the range of 1/10 to 10/1 byweight.

(8). An electrode as described above in (5), wherein the binder furthercomprises a polymer (Y) and a polymer (Z), both of which are the same asmentioned above, and wherein the ratio in content of the sum of thepolymer (X) plus the polymer (Y) to the polymer (Z) is in the range of5/1 to 1/5 by weight.

(9). A secondary battery having an electrode as described above in anyone of (5) to (8).

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in detail as for (1) the slurrycomposition for electrode, (2) the electrode and (3) the secondarybattery.

(1) Slurry Composition for Electrode

The slurry composition for electrode (hereinafter referred to merely as“slurry composition” when appropriate) of the present inventioncomprises an active material for electrode, a binder for bonding theactive material to a collector, and a liquid medium.

The binder in the slurry composition of the present invention comprisesas an indispensable ingredient a polymer (X) comprising repeating unitsderived from acrylonitrile or methacrylonitrile and repeating unitsderived from at least one kind of a monomer (hereinafter referred to as“second monomer” when appropriate) selected from 1-olefins and compoundsrepresented by the following general formula (1):CH₂═CR¹—COOR²   (1)wherein R¹ represents a hydrogen atom or a methyl group and R²represents an alkyl group.

The amount of the repeating units derived from acrylonitrile ormethacrylonitrile in the polymer (X) is in the range of 60 to 95% bymole, preferably 65 to 90% by mole, based on the total amount of polymer(X). If the amount of acrylonitrile or methacrylonitrile units is toosmall, the degree of swelling with en electrolyte liquid is large withthe result of reduction of the retention of bonding force of binder anddeterioration of the cycle characteristics of battery. In contrast, ifthe amount of acrylonitrile or methacrylonitrile units is too large, thebond properties of an active material become poor.

The amount of the repeating units derived from the second monomer in thepolymer (X) is in the range of 5 to 30% by mole, preferably 10 to 25% bymole. If the amount of the second monomer units is too small, thebonding force of an active material becomes poor, and the slurrycomposition is difficult to uniformly coat on a collector. In contrast,if the amount of the second monomer units is too large, the bondingforce of an active material tends to become poor, and the degree ofswelling with an electrolyte liquid is liable to be large.

The process for producing the polymer (X) is not particularly limited.For example, acrylonitrile or methacrylonitrile can be copolymerizedwith the second monomer by a conventional polymerization procedure suchas emulsion polymerization, suspension polymerization, dispersionpolymerization, solution polymerization or bulk polymerization.

As specific examples of the 1-olefin used as a second monomer, there canbe mentioned ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-buteneand 1-hexene. Of these, 1-olefins having 2 to 4 carbon atoms such asethylene, propylene and 1-butene are preferable. Ethylene is especiallypreferable.

As specific examples of the compound of formula (1) used as a secondmonomer, there can be mentioned acrylic acid alkyl esters such as methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butylacrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexylacrylate, 2-ethylhexyl acrylate and lauryl acrylate; and methacrylicacid alkyl esters such as methyl methacrylate, ethyl methacrylate,propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate,isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate,n-hexyl methacrylate, 2-ethylhexyl methacrylate and lauryl methacrylate.

Of these, the compounds of formula (1) with R² having not larger thanthree carbon atoms are preferable. Methyl acrylate and methylmethacrylate are especially preferable.

The repeating units of a second monomer may also be formed bycopolymerizing a conjugated diene monomer such as butadiene as a part ofthe raw material monomers, and hydrogenating the conjugated dienemonomer units in the thus-obtained copolymer. As specific examples ofthe conjugated diene monmer, there can be mentioned 1,3-butadiene,2-methyl-1,3-butadiene (i.e., isoprene), 2,3-dimethyl-1,3-butadiene and1,3-pentadiene.

The second monomer forming the repeating units thereof may be usedeither alone or as a combination of at least two thereof.

The polymer (X) may comprise repeating units derived from othercopolymerizable monomers provided that the polymer (X) can be dissolvedin the liquid medium used in the slurry composition of the presentinvention.

As specific examples of such copolymerizable monomers, there can bementioned acylic acid alkyl esters and methacrylic acid alkyl esters,the alkyl group of which has a hydroxyl group, such as hydroxypropylacrylate and hydroxypropyl methacrylate; crotonic acid esters such asmethyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate,isobutyl crotonate, n-amyl crotonate, isoamyl crotonate, n-hexylcrotonate, 2-ethylhexyl crotonate and hydroxypropyl crotonate;methacrylic acid esters having an amino group such as dimethylaminoethylmethacrylate and diethylaminoethyl methacrylate; methacrylic acid estershaving an alkoxyl group such as methoxypolyethylene glycolmonomethacrylate; acrylic acid alkyl esters and methacrylic acid esters,which have an alkyl group with a substituent such as a phosphoric acidresidue, a sulfonic acid residue and a boric acid residue; ethylenicallymonocarboxylic acids such as acrylic acid, methacrylaic acid, crotonicacid and isocrotonic acid; and unsaturated dicarboxylic acids such asmaleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconicacid and itaconic acid, and acid anhydrides thereof.

These copolymerizable monomers may be used either alone or as acombination of at least two thereof. The total amount of these monomersis not larger than 35% by mole and preferably not larger than 20% bymole.

The polymer (X) usually has a glass transition temperature (Tg) higherthan 0° C., preferably in the range of 50 to 90° C. When the Tg ofpolymer (X) is too low, it is often difficult to enhance the electrodedensity to the desired extent by pressing an electrode.

The slurry composition for electrode of the present invention maycomprise as a binder the polymer (X) alone, or other polymer, inaddition to the polymer (X). The polymer which can be used incombination with the polymer (X) is not particularly limited. Apreferable polymer used in combination with the polymer (X) is a polymer(Y) having a glass transition temperature (Tg) in the range of −80 to 0°C. and containing not larger than 5% by weight ofN-methyl-pyrrolidone-insoluble matter (N-methyl-pyrrolidone ishereinafter abbreviated to as “NMP” when appropriate). The content ofNMP-insoluble matter in the polymer (Y) is not larger than 5% by weight,preferably not larger than 3% by weight and more preferably not largerthan 1% by weight. By the use of the polymer (Y) in combination with thepolymer (X), solid content such as an active material in the slurrycomposition is not readily precipitated and the stability of the slurrycomposition is enhanced.

The content of NMP-insoluble matter is determined by a procedure wherein0.2 g of a polymer is immersed in 20 milli-liter of NMP at a temperatureof 60° C. for 72 hours, the immersed polymer is filtered through a sievewith 80 meshes, and the polymer residue on the sieve is dried andweighed. The content of NMP-insoluble matter is expressed by a ratio in% of the weight of the dried polymer to the weight of polymer asmeasured before the immersion in NMP.

The polymer (Y) has a Tg in the range of −80 to 0° C., preferably −60 to−5° C., and more preferably −40 to −10° C. If the Tg of polymer (Y) istoo high, a mixed material layer comprised of polymer (Y) and an activematerial (which layer is hereinafter referred to as “mixed materiallayer” when appropriate), formed on a collector, has a poor flexibility,and, when a cycle of charge and discharge of a battery is repeated,cracks tend to occur in the mixed material layer and the active materialis liable to be separated from the collector. In contrast, if the Tg ofpolymer (Y) is too low, the capacity of battery is liable to be reduced.

The monomer units constituting the polymer (Y) are not particularlylimited, but a monomer not containing fluorine is preferably used. Asspecific examples of the monomer, there can be mentioned α-olefins suchas ethylene, propylene, 1-butene, 1-pentene, isobutene and3-methyl-1-butene; acrylic acid esters such as ethyl acrylate, n-propylacrylate, butyl acrylate, isobutyl acrylate, n-octyl acrylate,2-ethylhexyl acrylate, methoxyethyl acrylate and ethoxyethyl acrylate;methacrylic acid esters such as n-octyl methacrylate, n-decylmethacrylate and n-lauryl methacrylate; conjugated dienes such as2-methyl-1,3-butadiene (i.e., isoprene), 2,3-dimethyl-1,3-butadiene,1,3-pentadiene and 1,3-hexadiene; and unsaturated nitrile compounds suchas acrylonitrile and methacrylonitrile.

The polymer (Y) may be a block copolymer or a random copolymer.

As specific examples of the polymer (Y), there can be mentioned anacrylonitrile-butadiene copolymer and its hydrogenation product, anethylene-methyl acrylate copolymer, a butadiene-methyl acrylatecopolymer, a styrene-butadiene copolymer, butadiene rubber, anethylene-propylene-non-conjugated diene terpolymer (EPDM) and anethylene-vinyl alcohol copolymer. Of these, a hydrogenation product ofan acrylonitrile-butadiene copolymer is especially preferable.

The process for producing the polymer (Y) is not particularly limited.For example, a conventional polymerization procedure such as emulsionpolymerization, suspension polymerization, dispersion polymerization orsolution polymerization can be adopted.

Another preferable example of the polymer which can be used incombination with the polymer (X) is a polymer (Z) having a glasstransition temperature (Tg) in the range of −80 to 0° C. and containingat least 50% by weight of NMP-insoluble matter. By using the polymer(Z), the total binder can be appropriately dissolved in a liquid mediumto an extent such that the slurry composition has a high viscositysuitable for coating. Further, when the slurry composition is coated,undissolved binder portion in the binder keeps a fibrous or particulateform in the coating so that the surface of an active material is notcompletely covered with the binder, and a cell reaction is notprevented.

The polymer (Z) has a Tg in the range of −80 to 0° C., preferably −60 to−5° C., and more preferably −50 to −10° C. If the Tg of polymer (Z) istoo high, an electrode has poor flexibility and, when a cycle of chargeand discharge of a battery is repeated, an active material is liable tobe separated from the collector. In contrast, if the Tg of polymer (Z)is too low, the capacity of battery is liable to be reduced.

The monomer units constituting the polymer (Y) are not particularlylimited, and, monomers used for producing the polymer (X) and thepolymer (Y) can also be used for producing the polymer (Z). As specificexamples of the monomer for giving the polymer (Z) having theabove-mentioned Tg, there can be mentioned acrylic acid esters such asethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate,n-octyl acrylate and 2-ethylhexyl acrylate; methacrylic acid esters suchas n-octyl methacrylate, n-decyl methacrylate and n-lauryl methacrylate;and conjugated dienes such as butadiene and isoprene.

The content of NMP-insoluble matter in the polymer (Z) is at least 50%by weight, preferably at least 60% by weight and more preferably atleast 70% by weight. If the content of NMP-insoluble matter is toosmall, retention of bond properties of an active material is reduced andthe capacity of battery tends to be reduced when a cycle ofcharge-discharge is repeated.

To give a polymer (Z) containing at least 50% by weight of NMP-insolublematter, a polyfunctional ethylenically unsaturated monomer is preferablyused as a part of the monomers for polymer (Z). The amount of thepolyfunctional ethylenically unsaturated monomer is usually in the rangeof 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on thetotal monomers used for the polymer (Z).

As specific examples of the polyfunctional ethylenically unsaturatedmonomer, there can be mentioned divinyl compounds such asdivinylbenzene, dimethacrylic acid esters such as ethylenedimethacrylate, diethylene glycol dimethacrylate and ethylene glycoldimethacrylate; trimethacrylic acid esters such as trimethylolpropametrimethacrylate; diacrylic acid esters such as diethylene glycoldiacrylate and 1,3-butylene glycol diacrylate; and triacrylic acidesters such as trimethylolpropane triacrylate.

In the case when a conjugated diene such as butadiene or isoprene iscopolymerized for the preparation of the polymer (Z), a crosslinkedcopolymer as the polymer (Z) can be obtained by appropriately choosingthe polymerization conditions such as the polymerization temperature,the polymerization conversion and the amount of molecular weightmodifier.

As specific examples of the polymer (Z) having the above-mentionedcharacteristics, there can be mentioned acrylic rubbers such as a2-ethylhexyl acrylate-methacrylic acid-methacrylonitrile-diethyleneglycol dimethacrylate copolymer, a butylacrylate-acrylonitrile-diethylene glycol dimethacrylate copolymer and abutyl acrylate-acrylic acid-trimethylolpropane trimethacrylatecopolymer; and diene rubbers such as an acrylonitrile-butadienecopolymer, butadiene rubber and a methyl methacrylate-butadienecopolymer. Of these, acrylic rubbers are preferable.

The polymer (Z) preferably has a particle diameter in the range of 0.005to 1,000 μm, more preferably 0.01 to 100 μm and especially preferably0.05 to 10 μm. If the polymer (Z) has too large particle diameter, theamount of binder is increased with the result in an increase of theinternal resistance. In contrast, if the polymer (Z) has too smalldiameter, the active material surface is liable to be covered with thebinder, leading to inhibition of cell reaction.

By the particle diameter as mentioned herein, we mean average particlediameter as determined as an arithmetic average value of particlediameter as measured using a transmission electron micrograph on 100particles sampled in random.

The procedure for producing the polymer (Z) is not particularly limited,and the polymer (Z) can be produced by a conventional polymerizationsuch as emulsion polymerization, suspension polymerization, dispersionpolymerization or solution polymerization. An emulsion polymerizationprocedure is especially preferable because the diameter of polymersdispersed in a liquid medium can be easily controlled.

In the case when the polymer (Y) or the polymer (Z) is used incombination with the polymer (X), the relative amounts of these polymersare not particularly limited, but the ratios by weight of X/Y and X/Zare usually in the range of 1/10 to 10/1, preferably 1/5 to 5/1 and morepreferably 1/3 to 3/1.

The three kinds of polymers (X), (Y) and (Z) may be used in combination.In this case, the ratio by weight of the sum of polymer (X) plus polymer(Y) to polymer (Z) is preferably in the range of 1/5 to 5/1, morepreferably 1/3 to 3/1 and especially preferably 1/2 to 2/1. When theamount of polymer (Z) is too large, the binding force is increased, butthe fluidity of a slurry composition is reduced and a mixed materiallayer formed on an electrode tends to have poor surface smoothness.

The amount of the total binders used in the present invention ispreferably in the range of 0.1 to 5 parts by weight, more preferably 0.2to 4 parts by weight and especially in the range of 0.5 to 3 parts byweight, based on 100 parts by weight of the active material. When theamount of the total binders is too small, an active material tends to beseparated from an electrode. In contrast, when the amount of the totalbinders is too large, an active material is liable to be completelycovered with the binder, leading to inhibition of cell reaction.

The liquid medium used for the slurry composition for a secondarybattery electrode of the present invention is not particularly limitedprovided that it is capable of dissolving the polymer (X), but, theliquid medium preferably has a boiling point at normal pressure in therange of 80° C. to 350° C. and more preferably 100° C. to 300° C.

As specific examples of the liquid medium, amides such asN-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethyl-formamidecan be mentioned. Of these, N-methylpyrrolidone is especially preferablein view of good coatability on a collector and good dispersibility ofpolymer (Z).

The amount of liquid medium in the slurry composition of the presentinvention is appropriately chosen depending upon the kind of a binder,an active material for electrode (mentioned below) and an electricalconductivity-imparting material so as to give a slurry compositionhaving a viscosity suitable for coating. The total solid content ofbinder, active material for electrode, and electricalconductivity-imparting material in the slurry composition is preferablyin the range of 50 to 95% by weight, more preferably 70 to 90% byweight.

The active material for electrode used in the slurry composition of thepresent invention is appropriately chosen depending upon the kind of anelectrode and a capacitor. The slurry composition of the presentinvention can be used for the preparation of a positive electrode and anegative electrode. The slurry composition is preferably used for apositive electrode, especially preferably for a positive electrode of alithium ion secondary battery.

In the case when the slurry composition is used for an electrode of alithium ion secondary battery, any active material for electrode can beused provided that it is capable of being used for general lithium ionsecondary batteries. As specific examples of the active material for apositive electrode, there can be mentioned lithium-containing compositemetal oxides such as LiCoO₂, LiNiO₂, LiMnO₂ and LiMn₂O₄; transitionmetal sulfides such as TiS₂, TiS₃ and amorphous MoS₃; and transitionmetal oxides such as Cu₂V₂O₃, amorphous V₂O—P₂O₅, MoO₃, V₂O₅ and V₆O₁₃.Electrically conductive polymers such as polyacetylene andpoly-p-phenylene can also be used as the active material for electrode.

As specific examples of the active material for a negative electrode,there can be mentioned carbonaceous materials such as amorphous carbon,graphite, natural graphite, meso-carbon micro-beads (MCMB) and pitchcarbon fiber; and electrically conductive polymers such as polyacene.The shape and size of the active material are not particularly limited,and active materials having an electrical conductivity-impartingmaterial deposited on the surface thereof by a mechanical modifyingmethod can also be used.

In the case when the slurry composition is used for an electrochemicalcapacitor, any active material for electrode can be used provided thatit is capable of being used for general electrochemical capacitor. As aspecific example of the active material used for a positive electrodeand a negative electrode, active carbon can be mentioned.

An electrical conductivity-imparting material can be incorporated in theslurry composition of the present invention, according to the need. Asspecific examples of the electrical conductivity-imparting material fora lithium ion secondary battery, carbon such as graphite and activecarbon can be mentioned.

As specific examples of the electrical conductivity-imparting materialfor a nickel-hydrogen secondary battery, cobalt oxide is used for apositive electrode and nickel powder, cobalt oxide, titanium oxide andcarbon are used for a negative electrode.

As specific examples of the carbon used for a lithium ion secondarybattery and a nickel-hydrogen secondary battery, there can be mentionedacetylene black, furnace black, graphite, carbon fiber and fullerene. Ofthese, acetylene black and furnace black are preferable.

The amount of electrical conductivity-imparting material is usually inthe range of 1 t 20 parts by weight, preferably 2 to 10 parts by weight,based on 100 parts by weight of the active material for electrode.

The above-mentioned slurry composition may comprise an additive such asa viscosity modifier and a fluidizing agent, according to the need.

The slurry composition for electrode of the present invention isprepared by mixing together the above-mentioned ingredients. The mixingprocedure and mixing order are not particularly limited. For example,polymer (Z) is dispersed in a liquid medium, and polymer (X), polymer(Y), an active material for electrode and an electricalconductivity-imparting material are added to the dispersion of polymer(X), and the mixture is stirred by a mixer. The extent of dispersion canbe determined by a particle gauge. Preferably the mixing for dispersionis carried out to an extent such that the dispersion does not containagglomerates having a particle diameter larger than 100 μm. As specificexamples of the mixer, there can be mentioned a ball mill, a sand mill,a pigment disperser, a pulverizer, an ultrasonic disperser, ahomogenizer, a planetary mixer and a hovert mixer.

(2) Electrode

The electrode of the present invention comprises a mixed material layercomprising at least a binder and an active material for electrode, whichlayer is bonded to a collector.

The collector used is not particularly limited provided that it iscomposed of an electrically conductive material. The collector used fora lithium ion secondary battery is usually composed of metal such asiron, copper, aluminum, nickel or stainless steel. In the case whenaluminum is used for a positive electrode and copper is used for anegative electrode, the binder contained in the slurry composition ofthe present invention manifests the most marked binding effect. Theshape of a collector for a lithium ion secondary battery is also notparticularly limited, and the collector is usually used in a sheet formhaving a thickness of about 0.001 to 0.5 mm.

The collector used for a nickel-hydrogen secondary battery includes, forexample, punched metal, expanded metal, metallic wire, sintered metalbody with network structure of fibrous metal and metal-plated resinplate.

The electrode of the present invention can be made by coating acollector with the slurry composition for electrode of the presentinvention, and drying the coating, whereby a mixed material layercomprising a binder and an active material for electrode, and optionalingredients such as an electrical conductivity-imparting material and athickening agent, is bonded to the surface of collector.

The procedure of coating a collector with the slurry composition is notparticularly limited. The collector can be coated with the slurrycomposition by a conventional coating procedure such as doctor-bladecoating, dip coating, reverse-roll coating, direct-roll coating, gravurecoating, extrusion coating and brush coating. The amount of the slurrycomposition applied is also not particularly limited, and is usuallysuch that the thickness of the mixed material layer comprising an activematerial for electrode and a binder, formed by removing a liquid mediumby drying a coating of the slurry composition, has a thickness of arange of 0.005 mm to 5 mm, preferably 0.01 mm to 2 mm. The procedure fordrying an as-formed coating is not particularly limited, and includes,for example, warm-air drying, hot-air drying, low-humid-air drying,vacuum drying, infrared drying, far-infrared drying and electronradiation drying. The rate of drying should be chosen so that the liquidmedium used is removed as soon as possible, but occurrence of stresscrack in the mixed material layer due to stress concentration, andseparation of the mixed material layer from the collector can beavoided.

The coated collector can be pressed, if desired, to enhance the densityof the active material in an electrode. The pressing can be carried out,for example, by a mold pressing and a roll pressing.

(3) Secondary Battery

The secondary battery of the present invention comprises theabove-mentioned electrode and an electrolyte solution, and, according tothe need, a separator and other elements. The secondary battery can bemanufactured by an ordinary procedure. For example, a positive electrodeand a negative electrode are superposed with a separator interposedbetween the two electrodes, and the thus-formed assembly is wound orfolded and then inserted into a vessel for battery. An electrolytesolution is introduced into the vessel, and then the vessel is sealed.According to the need, expanded metal, an over-current-preventingelement such as a fuse or a PTC element, or a lead plate can be insertedto avoid a pressure increase within the battery andover-charge-discharge of the battery. The shape of the secondary batteryis not particularly limited, and is, for example, coin-shape,button-shape, sheet-shape, cylindrical shape, rectangular shape and flatshape.

The electrolyte solution is in any form of gel or liquid. A suitableelectrolyte solution can appropriately be chosen depending upon theparticular active material used for a positive electrode or a negativeelectrode so as to obtain the desired battery performances.

The electrolyte for a lithium ion secondary battery includes knownlithium salts. As specific examples of the electrolyte, there can bementioned LiClO₄, LiBF₄, LiPF₆, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiB₁₀Cl₁₀,LiAlCl₄, LiCl, LiBr, LiB(C₂H₅)₄, LiCF₃SO₃, LiCH₃SO₃, LiC₄F₉S₃,Li(CF₃SO₂)₂N and lower aliphatic carboxylic acid lithium salt.

The liquid medium used for dissolving the electrolyte is notparticularly limited, and, as specific examples of the liquid medium,there can be mentioned carbonates such as propylene carbonate, ethylenecarbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonateand diethyl carbonate; lactones such as γ-butyrolactone; ethers such astrimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane,tetrahydrofuran and 2-methyltetrahydrofuran; and sulfoxides such asdimethylsulfoxide. These liquid mediums may be used either alone or as amixed liquid comprised of at least two kinds thereof.

The electrolyte for a nickel-hydrogen secondary battery includes, forexample, a conventional aqueous potassium hydroxide solution having aconcentration of 5 moles/liter or more.

The invention will now be described more specifically by the followingworking examples that by no means limit the scope of the invention. Inthe working examples, parts and % are by weight unless otherwisespecified.

(1) Degree of Swelling of Polymer with Solvent in Electrolyte Solution

A solution of 0.2 g of a polymer in 10 milli-liter ofN-methylpyrrolidone (NMP) was cast on a polytetrafluorethylene sheet,and then dried to give a cast polymer film. A square specimen having asize of 4 cm², cut from the cast polymer film, was weighed (weight A),and then immersed in a solvent of an electrolyte solution at atemperature of 60° C. After 72 hours' immersion, the specimen was takenand immediately weighed (weight B). The degree of swelling of polymerwith solvent in electrolyte solution was expressed by the ratio ofweight B as measured after immersion to weight A as measured beforeimmersion. As the solvent in an electrolyte solution, a mixed solventcomprised of ethylene carbonate, propylene carbonate, dimethylcarbonate, diethyl carbonate and ethylmethyl caronate (1:1:1:1:1 byvolume at 20° C.) was used.

(2) Content of Insoluble Matter in NMP

0.2 g of a polymer was immersed in 20 milli-liter of NMP at atemperature of 60° C. for 72 hours, and then, filtered through a sievewith 80 mesh size. The polymer on the sieve was dried and weighed. Thecontent of insoluble matter in NMP was expressed by the ratio of theweight of polymer as measured after immersion and drying, to the weightof polymer as measured before immersion.

(3) Glass Transition Temperature (Tg)

Tg of polymer was measured using a differential scanning calorimeter(DSC) at a temperature elevation rate of 10° C./min.

(4) Particle Diameter

Particle diameter of a polymer was measured on 100 polymer particlessampled at random, using a transmission electron microscope. Theparticle diameter was expressed by the number average value of 100particle diameters.

(5) Sedimentation in Slurry

A cyrindrical glass bottle having a height of 40 mm and a volume of 5 mlwas charged with a slurry composition so that the slurry composition inthe bottle had a height of 25 mm. The bottle was sealed and allowed tostand for 24 hours. A 5 mm top part of the slurry was taken and thesolid content is measured. The sedimentation in slurry was expressed bythe change % of solid concentration which was calculated from thefollowing equation.Change percentage=[1−(C1/C2)]×100wherein C1 is a solid content in the 5 mm top part of slurry as measuredafter 24 hours' standing, and C2 is a solid content as measured on theinitial slurry. The smaller the change percentage, the smaller thedegree of sedimentation in slurry.(6) Peel Strength

Manufacture of Positive Electrode

An aluminum foil having a thickness of 20 μm was uniformly coated with aslurry for positive electrode by a doctor blade. The coating was driedby a dryer at 120° C. for 45 minutes, and further dried under reducedpressure of 0.6 kPa MP at 120° C. for 2 hours. Then the coated foil waspressed by a twin-roll press to give a positive electrode having anelectrode density of 3.3 g/cm³.

Manufacture of Negative Electrode

A copper foil having a thickness of 18 μm was uniformly coated with aslurry for negative electrode by a doctor blade. The coating was driedin the same manner as in the positive electrode. The coated foil waspressed by a twin-roll press to a negative electrode having an electrodedensity of 1.4 g/cm³.

Measurement of Peel Strength

Each of the above-mentioned positive electrode and negative electrodewas cut into a rectangle with 2.5 cm width and 10 cm length, and acellophane tape was adhered on the surface of the rectangular electrode.The electrode was fixed, and the peel strength was measured by peelingthe tape at a peel angle of 180° and a peel rate of 50 mm/min. Themeasurement was made on 10 electrodes and the peel strength (N/cm) wasexpressed by the average value. With an increase in the peel strength,an active material for electrode becomes desirably difficult to separatefrom the collector.

(7) Capacity of Battery

Manufacture of Coin-Shaped Battery for Evaluation of Positive Electrode

In the evaluation of a positive electrode, lithium metal was used as anegative electrode.

The positive electrode, manufactured by the method mentioned above in(6), was cut into a circular shape having a diameter of 15 mm. A batterywas manufactured by using the circular positive electrode and a lithiummetal negative electrode, and a separator. The separator was sandwichedbetween the positive electrode and the lithium metal negative electrodeso that the two electrodes confronted to each other. The separator wascomprised of a circular porous polypropylene film having a diameter of18 mm and a thickness of 25 μm. An assembly composed of the positiveelectrode, the separator, and the negative electrode was placed in acoin-shaped outer casing having a diameter of 20 mm and a height of 1.8mm and made of a stainless steel sheet having a thickness of 0.25 mm andhaving a packing made of polypropylene. An expanded metal part wasplaced on the side of lithium metal negative electrode opposite to theseparator. An electrolyte solution was injected into the casing so thatno air remains within the casing. A stainless steel cap having athickness of 0.2 mm was placed on the thus-made assembly via apolypropylene packing. The stainless steel cap was fixed and theassembly-packed casing is sealed whereby a coin-shaped battery forevaluation of the positive electrode, having a diameter of 20 mm and athickness of about 2 mm is obtained. The electrolyte solution is asolution of LiPF₆ with a concentration of 1 mol/liter in a mixed liquidcomposed of ethylene carbonate/ethylmethyl carbonate at a mixing ratioof 1:2 by volume at 20° C.

Manufacture of Coin-Shaped Battery for Evaluation of Negative Electrode

In the evaluation of a negative electrode, lithium metal was used as apositive electrode.

The negative electrode, manufactured by the method mentioned above in(6), was cut into a circular shape having a diameter of 15 mm. A batterywas manufactured by using the circular negative electrode and a lithiummetal positive electrode, and a separator. The separator was sandwichedbetween the negative electrode and the lithium metal positive electrodeso that the two electrodes confronted to each other. An expanded metalpart was placed on the side of lithium metal positive electrode oppositeto the separator. By the same procedures as mentioned above for themanufacture of the coin-shaped battery for evaluation of positiveelectrode, a coin-shaped battery for evaluation of negative electrodewas manufactured. The separator and coin-shaped outer casing were thesame as those used for the manufacture of the coin-shaped battery forevaluation of positive electrode.

Measurement of Capacity of Battery

Using the coin-shaped batteries manufactured by the above-mentionedmethods, the positive electrode and the negative electrode wereevaluated to determine the capacity of battery. A charge-discharge testwas carried out while a cycle of charge and discharge was repeatedbetween 3V and 4.2V for the evaluation of a positive electrode andbetween OV and 1.2V for the evaluation of a negative electrode,respectively, at a predetermined temperature and a constant current rateof 0.1 C. The measurement of battery capacity was carried out as thedischarge capacity (initial discharge capacity) at the third cycle. Theunit of capacity was mAh/g of active material.

(8) Charge-Discharge Cycle Characteristics of Battery

In the same manner as the above-mentioned measurement of the initialdischarge capacity, the discharge capacity at the third cycle and thedischarge capacity at the 50th cycle were measured. The charge-dischargecycle characteristics were expressed by the ratio in percent of thedischarge capacity at the 50th cycle to the discharge capacity at thethird cycle. The larger this discharge capacity ratio, the smaller thereduction of battery capacity.

(9) Charge-Discharge Rate Characteristics of Battery

In the same manner as the above-mentioned measurement of the initialdischarge capacity, the discharge capacity at the third cycle wasmeasured at a constant current rate of 1 C. The charge-discharge ratecharacteristics were expressed by the ratio in percent of the dischargecapacity at the third cycle at a constant current rate of 1 C to thedischarge capacity at the third cycle at a constant current rate of 0.1C. The larger this discharge capacity ratio, the higher thecharge-discharge rate.

The composition, production method and properties of polymers (X),polymers (Y) and polymers (Z), used as a binder, are shown in Tables 1,2 and 3. Polymer (Y-1) in Table 2 is a hydrogenation product ofacrylonitrile-butadiene copolymer rubber. Ethylene units in thishydrogenation product were formed by hydrogenation of butadiene units.Polyvinylidene fluoride (PVDF) shown in Table 5 was #1100 available fromKureha Chem. Ind. Co., (NMP-insoluble matter content: below 0.1% byweight). TABLE 1 X-1 X-2 X-3 X-4 X-5 X-6 X-7 X-8 X-9 X-10 X-11Composition of polymer (mole %) Acrylonitrile 78 85 91 82 78 78 87 89 8082 84 Ethylene 22 15 9 — — 15 — — — 18 — Propylene — — — 18 — — — — — —16 1-Butene — — — — 22 — — — — — — Methyl acrylate — — — — — 7 13 — 14 —— Methyl methacrylate — — — — — — — 11 6 — — Production method andproperties of polymer Polym'n method *1 sol sol sol sol sol sol sus sussus sol sol Tg(° C.) 68 78 85 81 62 53 80 98 80 74 83 SD in liq medium*2 1.5 1.3 1.3 1.6 1.7 1.8 1.7 1.7 1.9 1.5 1.6 X-12 X-13 X-14 X-15 X-16X-17 X′-1 X′-2 X′-3 X′-4 Composition of polymer (mole %) Acrylonitrile88 80 92 90 85 80 100 35 63 30 Ethylene — — — 10 — — — — 23 — Propylene— — — — — 20 — — — — 1-Butene 12 — — — — — — — — — Methyl acrylate — 20— — 15 — — 42 — 40 Methyl methacrylate — — 8 — — — — 23 14 30 Productionmethod and properties of polymer Polym'n method *1 emu sus sus sol solsol sus sus sol sus Tg(° C.) 78 72 98 86 78 80 97 59 73 63 SD in liqmedium *2 1.6 1.8 1.4 1.3 1.8 1.7 1.1 7.2 5.7 9.6*1 Polymerization method, sol: solution polymerization, sus:suspensition polymerization, emu: emulsion polymerization*2 Swelling degree of polymer with liquid medium for electrolyte

TABLE 2 Y-1 Y-2 Y-3 Y-4 Composition of polymer (mole %) Ethylene 75 45 —— Butadiene — — 60 — Methyl acrylate — 55 40 — 2-Ethylhexyl acrylate — —— 68 Methacrylic acid — — — 6 Styrene — — — 26 Acrylonitrile 25 — — —Properties of polymer Tg(° C.) −22 −13 −10 −43 NMP-insoluble *1 (%) <0.1<0.1 <0.1 <0.1*1 Content of NMP-insoluble matter

TABLE 3 Z-1 Z-2 Z-3 Z-4 Z-5 Z-6 Z-7 Z-8 Z-9 Composition of polymer (mole%) Ethyl acrylate — — — 70 — — — — — Butyl acrylate — 55 — — 82 — — — —2-Ethylhexyl acrylate 72 — — — — 76 62 72 76 Methyl methacrylate — — — —— — 15 — — Acrylonitrile — 44 61 — 15 — — — 20 Methacrylonitrile 20 — —— — 20 20 25 — Methacrylic acid 7 — — — 2 3 2 — — Styrene — — — 28 — — —— — Butadiene — — 38.9 — — — — — — Diethylene glycol 1 1 — 2 1 1 1 3 4dimethacrylate Trimethylenepropane — — 0.1 — — — — — — trimethacrylateProperties of polymer Tg(° C.) −47 −42 −25 15 −40 −47 −30 −51 −54NMP-insoluble *1 (%) 85 89 86 98 88 85 82 95 97 Particle diameter (μm)0.20 0.20 0.08 0.13 0.12 0.15 0.16 0.23 0.12*1 Content of NMP-insoluble matter

EXAMPLE 1

To a solution of 1.5 parts of polymer (X-1) in NMP, 100 parts of lithiumcobaltate (LiCoO₂) as active material for electrode and 3 parts ofacetylene black (HS-100 available from Denki Kagaku Kogyou K.K.) aselectrical conductivity-imparting agent were added, and NMP was furtheradded in an amount such that the mixture had a solid content of 77%. Themixture was stirred by a planetary mixer to give a uniform slurry forpositive electrode. Using the slurry, a positive electrode, and furthera secondary battery were manufactured. Peel strength of the electrode,and properties of the secondary battery were evaluated at 20° C. Theresults are shown in Table 4.

EXAMPLES 2-8, COMPARATIVE EXAMPLES 1-3

By the same procedures as described in Example 1, slurry compositionswere prepared except that polymers shown as polymer (X) in Table 4 wereused with all other conditions remaining the same. Using the slurrycompositions, positive electrodes and further secondary batteries weremanufactured. Properties of the electrodes and the secondary batterieswere evaluated. The results are shown in Table 4.

EXAMPLE 9

To a solution of 5 parts of polymer (X-9) in NMP, 95 parts of MCMB asactive material for electrode was added, and NMP was further added in anamount such that the mixture had a solid content of 68%. The mixture wasstirred to give a uniform slurry for negative electrode. Using theslurry, a positive electrode, and further a secondary battery weremanufactured. Peel strength of the electrode, and properties of thesecondary battery were evaluated at 25° C. The results are shown inTable 4. TABLE 4 Example Comp. Ex. 1 2 3 4 5 6 7 8 9 1 2 3 Kind ofpolymer X-1 X-2 X-3 X-4 X-5 X-6 X-7 X-8 X-9 X′-1 X′-2 X′-3 Kind ofelectrode *1 P P P P P P P P N P P P Peel strength (N/cm) 0.27 0.24 0.230.28 0.27 0.28 0.24 0.22 0.23 0.10 0.12 0.15 Battery capacity 142 144144 143 143 141 142 141 330 138 121 126 (mAh/g) Cycle characs *2 (%) 6764 61 66 67 67 63 61 63 38 34 40 Rate characs *3 (%) 48 41 42 44 46 4344 41 42 28 21 24*1 P: positive electrode, N: negative electrode*2 Charge-discharge cycle characteristics of battery*3 Charge-discharge rate characteristics of battery

EXAMPLE 10

To a solution of 0.6 parts of polymer (Y-1) in NMP, 3 parts of acetyleneblack (HS-100 available from Denki Kagaku Kogyou K.K.) as electricalconductivity-imparting agent was added, and the mixture was stirred by apigment dispersing apparatus. NMP was added to prepare a carbon coatingliquid having a solid content of 35%.

100 parts of lithium cobaltate and a solution of 0.2 part of polymer(X-15) in NMP were placed in a planetary mixer equipped with two pairsof hook-type rotor blades. Further, 12.8 parts of the above-mentionedcarbon coating liquid, and NMP were added to prepare a slurry having asolid content of 83%. The slurry was stirred for one hour, and NMP wasfurther added to reduce the solid content to 78%. The resulting slurrywas stirred for 10 minutes to give a slurry composition for a positiveelectrode of a lithium ion secondary battery. The slurry composition hada viscosity of 3,660 mPa.s and exhibited a change in slurrysedimentation of 3.3% as measured after 24 hours. Using the slurrycomposition, an electrode and further a secondary battery weremanufactured. Properties of the electrode and the secondary battery wereevaluated. The results are shown in Table 5.

EXAMPLES 11-14, COMPARATIVE EXAMPLES 4-8

By the same procedures as described in Example 10, slurry compositionswere prepared except that ingredients shown in Table 5 were used inamounts shown in Table 5 with all other conditions remaining the same.Using the slurry compositions, electrodes and further secondarybatteries were manufactured. Properties of the electrodes and thesecondary batteries were evaluated. The results are shown in Table 5.

In Comparative Example 4, the binding force was insufficient and cracksoccurred in the electrode, and therefore, properties of the secondarybattery could not be measured. TABLE 5 Example Comparative Example 10 1112 13 14 4 5 6 7 8 Polymer X X-15 X-15 X-16 X-16 X-17 — — — — X′-4Amount (parts) 0.2 0.2 0.4 0.2 0.5 — — — — 0.2 Polymer Y Y-1 Y-2 Y-1 Y-3Y-1 — — Y-1 Y-3 Y-2 Amount (parts) 0.6 0.6 0.4 0.6 0.3 — — 0.8 0.4 0.6Other binder *1 — — — — — PVDF PVDF — PVDF — Amount (parts) — — — — — 26 — 0.4 — Slurry sedimentation *2 (%) 3.3 2.8 2.4 3.5 1.1 10.6 2.2 1.29.3 5.5 Peel strength (N/cm) 0.25 0.21 0.32 0.19 0.25 0.06 0.24 0.110.08 0.18 Battery capacity (mAh/g) 144 141 142 140 140 NM *3 132 141 130135 Cycle characteristics *4 (%) 72 69 73 66 70 NM *3 55 44 42 47 Ratecharacteristics *5 (%) 68 66 67 64 65 NM *3 30 63 38 42*1 PVDF: Polyvinylidene fluoride*2 Sedimentation of slurry*3 Not measurable*4 Charge-discharge cycle characteristics of battery*5 Charge-discharge rate characteristics of battery

EXAMPLE 15

A solution of 0.8 part of polymer (X-10) in NMP was mixed together witha dispersion of 1.5 parts of polymer (Z) in NMP. To the mixed liquid,100 parts of lithium cobaltate as active material for electrode and 5parts of acetylene black (HS-100 available from Denki Kagaku KogyouK.K.) as electrical conductivity-imparting agent were added, and NMP wasfurther added in an amount such that the mixture had a solid content of75%. The mixture was stirred by a planetary mixer to give a uniformslurry for positive electrode. Using the slurry, a positive electrode,and further a secondary battery were manufactured. Peel strength of thepositive electrode, and capacity of the secondary battery at 30° C. andcharge-discharge cycle characteristics and charge-discharge ratecharacteristics were evaluated at 60° C. The results are shown in Table6.

EXAMPLES 16-22, COMPARATIVE EXAMPLES 9, 10

The procedures as described in Example 15 were repeated except that thepolymers shown in Table 6 were used with all other conditions remainingthe same. The results of evaluation of properties of electrodes andsecondary batteries are shown in Table 6. TABLE 6 Example Comp. Ex. 1516 17 18 19 20 21 22 9 10 Polymer X X-10 X-11 X-12 X-13 X-14 X-10 X-10X-10 X′-1 X′-2 Amount (parts) 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8Polymer Z Z-1 Z-1 Z-1 Z-1 Z-1 Z-2 Z-3 Z-4 Z-1 Z-1 Amount (parts) 1.5 1.51.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Peel strength (N/cm) 0.34 0.32 0.36 0.330.30 0.33 0.32 0.29 0.21 0.24 Battery capacity (mAh/g) 144 142 142 141141 143 142 138 135 132 Cycle characteristics *1 (%) 65 66 62 60 61 6563 52 40 32 Rate characteristics *2 (%) 44 40 43 40 42 42 44 35 29 25*1 Charge-discharge cycle characteristics of battery*2 Charge-discharge rate characteristics of battery

EXAMPLE 23

By procedures similar to those as described in Example 10, a slurrycomposition for an electrode for lithium ion secondary battery wasprepared wherein the following procedures are carried out with all otherconditions remaining the same. 100 parts of lithium cobaltate and 0.4part of polymer (Z-5) were mixed together with NMP to prepare a liquiddispersion having a solid content of 87%. A solution of 0.2 part ofpolymer (X-15) in NMP and a solution of 0.2 part of polymer (Y-1) in NMPwere mixed together with 3 parts of acetylene black to prepare a carboncoating liquid. The carbon coating liquid was added to theabove-mentioned liquid dispersion to prepare the slurry composition.

The slurry composition for an electrode for lithium ion secondarybattery had a viscosity of 2,400 mPa.s and exhibited a change in slurrysedimentation of 2.5%. Using the slurry composition, an electrode andfurther a secondary battery were manufactured. Properties of theelectrode and the secondary battery were evaluated at 25° C. The resultsare shown in Table 7. TABLE 7 Example 23 24 25 26 27 28 Polymer X X-15X-16 X-16 X-17 X-7 X-1 Amount (parts) 0.2 0.2 0.3 0.4 0.2 0.2 Polymer YY-1 Y-2 Y-2 Y-1 Y-1 Y-1 Amount (parts) 0.2 0.3 0.1 0.2 0.2 0.2 Polymer ZZ-5 Z-5 Z-6 Z-7 Z-8 Z-9 Amount (parts) 0.4 0.3 0.4 0.2 0.4 0.4 Slurry2.5 2.1 2.8 2.7 2.2 2.5 sedimentation (%) Peel strength 0.32 0.31 0.330.30 0.32 0.33 (N/cm) Battery 142 143 145 142 144 143 capacity (mAh/g)Cycle 68 66 70 72 68 67 character- istics *1 (%) Rate 65 66 62 62 66 64character- istics *2 (%)*1 Charge-discharge cycle characteristics of battery*2 Charge-discharge rate characteristics of battery

EXAMPLES 24-28

Slurry compositions were prepared by the same procedures as described inExample 23 except that the ingredients shown in Table 7 were used inamounts shown in Table 7 with all other conditions remaining the same.Using the slurry compositions, electrodes and further secondarybatteries were manufactured. Properties of the slurry compositions, theelectrodes and the secondary batteries were evaluated. The results areshown in Table 7.

As seen from the above-mentioned working examples, an electrodemanufactured from the slurry composition of the present inventionexhibits a high peel strength and thus a polymer binder exhibits anenhanced binding performance even when the amount of a polymer binder issmall. A lithium ion secondary battery provided with this electrode hasa high capacity and exhibits good charge-discharge cycle characteristicsand good charge-discharge rate characteristics.

Industrial Applicability

The slurry composition for electrode of the present invention gives anelectrode exhibiting low degree of swelling with an electrolyte liquid,and a binder polymer in the electrode has a high binding performance.Therefore, the slurry composition is suitable for the manufacture ofvarious batteries and electrochemical capacitors.

The slurry composition is especially suitable for the manufacture of apositive electrode of a lithium ion secondary battery. The lithium ionsecondary battery provided with this electrode keeps a high capacity atrepetition of charge-discharge cycle, and exhibits good charge-dischargecycle characteristics and good charge-discharge rate characteristics.

1. A slurry composition for electrode comprising a binder, an activematerial for electrode, and a liquid medium, characterized in that thebinder comprises a polymer (X) comprising 60 to 95% by mole of repeatingunits derived from acrylonitrile or methacrylonitrile and 5 to 30% bymole of repeating units derived from at least one kind of a monomerselected from 1-olefins and compounds represented by the followinggeneral formula (1):CH₂═CR¹—COOR²   ( 1) wherein R¹ represents a hydrogen atom or a methylgroup and R² represents an alkyl group; and the liquid medium is capableof dissolving the polymer (X).
 2. The slurry composition for electrodeaccording to claim 1, wherein the binder further comprises a polymer (Y)having a glass transition temperature in the range of −80 to 0° C. andcontaining not larger than 5% by weight ofN-methyl-pyrrolidone-insoluble matter, and the ratio in content of thepolymer (X) to the polymer (Y) is in the range of 1/10 to 10/1 byweight.
 3. The slurry composition for electrode according to claim 1,wherein the binder further comprises a polymer (Z) having a glasstransition temperature in the range of −80 to 0° C. and containing atleast 50% by weight of N-methyl-pyrrolidone-insoluble matter, and theratio in content of the polymer (X) to the polymer (Z) is in the rangeof 1/10 to 10/1 by weight.
 4. The slurry composition for electrodeaccording to claim 1, wherein the binder further comprises a polymer (Y)and a polymer (Z), each of said polymers (Y) and (Z) having a glasstransition temperature in the range of −80 to 0° C., wherein the polymer(Y) contains no larger than 5% by weight ofN-methyl-pyrrolidoneinsoluble matter and the polymer (Z) contains atleast 50% by weight of N-methyl-pyrrolidoneinsoluble matter, and theratio in content of the sum of the polymer (X) plus the polymer (Y) tothe polymer (Z) is in the range of 5/1 to 1/5 by weight.
 5. A method ofmanufacturing a positive electrode of a lithium ion secondary battery,said method comprising using the slurry composition for an electrodeaccording to claim
 1. 6. The slurry composition for an electrodeaccording to claim 1, wherein the liquid medium is N-methyl-pyrrolidone.7. The slurry composition for an electrode according to claim 2, whereinthe polymer (Y) is a hydrogenation product of an acrylonitrile-butadienecopolymer.
 8. The slurry composition for an electrode according to claim3, wherein the polymer (Z) is an acrylic rubber.
 9. An electrodecomprising a mixed material layer comprising at least a binder and anactive material for electrode, which layer is bonded to a collector,characterized in that the binder comprises a polymer (X) comprising 60to 95% by mole of repeating units derived from acrylonitrile ormethacrylonitrile and 5 to 30% by mole of repeating units derived fromat least one kind of a monomer selected from 1-olefins and compoundsrepresented by the following general formula (1):CH₂═CR¹—COOR²   ( 1) wherein R¹ represents a hydrogen atom or a methylgroup and R² represents an alkyl group; and the liquid medium is capableof dissolving the polymer (X).
 10. The electrode according to claim 9,wherein the binder further comprises a polymer (Y) having a glasstransition temperature in the range of −80 to 0° C. and containing notlarger than 5% by weight of N-methyl-pyrrolidone-insoluble matter, andthe ratio in content of the polymer (X) to the polymer (Y) is in therange of 1/10 to 10/1 by weight.
 11. The electrode according to claim 9,wherein the binder further comprises a polymer (Z) having a glasstransition temperature in the range of −80 to 0° C. and containing atleast 50% by weight of N-methyl-pyrrolidone-insoluble matter, and theratio in content of the polymer (X) to the polymer (Z) is in the rangeof 1/10 to 10/1 by weight.
 12. The electrode according to claim 9,wherein the binder further comprises a polymer (Y) and a polymer (Z),both of which have a glass transition temperature in the range of −80 to0° C., wherein the polymer (Y) contains not larger than 5% by weight ofN-methyl-pyrrolidone-insoluble matter, the polymer (Z) contains at least50% by weight of N-methyl-pyrrolidone-insoluble matter, and the ratio incontent of the sum of the polymer (X) plus the polymer (Y) to thepolymer (Z) is in the range of 5/1 to 1/5 by weight.
 13. A secondarybattery having an electrode as claimed in claim
 9. 14. The slurrycomposition for an electrode according to claim 4, wherein the polymer(Y) is a hydrogenation product of an acrylonitrile-butadiene copolymer.15. The slurry composition for an electrode according to claim 4,wherein the polymer (Z) is an acrylic rubber.